Two main techniques are currently known for making electronic micropackages or modules designed for electronic memory cards.
In a first technique described in French Patent No. 2 488 446, for example, a strip of insulating material, such as polyethylene or an epoxy resin, is perforated so as to provide holes through which connection wires can pass to connect the semiconductor chip to electrical contact zones. A metal strip is laminated on the strip of insulating material, and is then removed by chemical etching so as to form electrical contact zones on which protective layers are deposited. The protective layers are gold layers deposited on the metal forming the contact zones, which is generally copper. Since copper is likely to be oxidized when exposed to the ambient atmosphere, the gold layers are deposited to prevent such oxidation. In a subsequent stage, the semiconductor chip is glued onto the strip of insulating material or into a window pre-cut in the strip together with the through holes. The semiconductor chip is then connected to the electrical contact zones via connection wires passing through the through holes. Finally, the semiconductor chip and the connection wires are protected against mechanical and chemical damage by a coating of epoxy resin obtained by molding or by merely depositing a drop of resin.
A second technique described in French Patent No. 2639763 includes mechanically cutting out a metal strip, curving it, and then overmolding insulating material onto it while leaving uncovered the cut-out zones in the metal strip, which zones constitute the electrical contact zones of the electronic module. The term "overmolding" describes forming a shape by merely pouring a molding material over an object, in contrast to "molding" which suggests the presence of a mold wherein the object is positioned in place before the mold is filled with molding material. The metal is thus held securely in the overmolded insulating material by means of the initial curving of the strip, thereby mechanically securing the cut-out metal zones. The insulating overmolding also forms a cup in which the semiconductor chip is glued and connected to the electrical contact zones via connection wires. Protecting the semiconductor chip and the connection wires is thus made considerably easier because it suffices merely to fill the cup with a liquid resin.
Unfortunately, these two known techniques suffer from various drawbacks when large-sized semiconductor chips are to be protected. With the first technique, the difficulty lies, firstly, in the cost of the resulting micropackage due in particular to the chemical etching step during which the laminated metal strip is etched and, secondly, in the protective coating for protecting the semiconductor chip and the connection wires because it is very difficult to coat over a large area without increasing its thickness to a prohibitive extent. With the second technique, the difficulty lies in forming the cup bottom which must be very fine but must extend over a large area with good surface evenness.